I ran the code accompanied with Introduction to 3D Game Programming with DirectX 12 on my computer, but it always throw exception like this: 
The Chinese there means something like "Invalid argument".
The return value of mCommandList->close() should be -2147024809 in decimal, it's a HRESULT value. I've encountered similar problem in my own code many times, and I recorded the return value.
But the code runs well months earlier without any modification. I wonder if some upgrade of my win10 may be the cause.
Thanks for your suggestion.